1. Field of the Invention
The present invention relates to a printed wiring board on which a quad flat package integrate circuit (IC) is mounted by soldering using a jet solder bath.
2. Description of the Related Art
Generally, printed wiring boards are increasingly required to be assembled at a high component-mounting package density, and therefore, narrow-pitch quad flat package ICs and the like have to be mounted on a board. On the other hand, ecologically friendly lead-free solder is rapidly proceeding to practical use. However, the lead-free solder has poor solderability compared to lead-containing eutectic solder that has conventionally been used. For that reason, a short circuit due to the solder may occur between lead terminals of a quad flat package IC and the like.
Conventionally, as this type of printed wiring board, there has been a printed wiring board in which an eyelet is provided on one of the spaces between a forward soldering land group and a rearward soldering land group, and grid-formed solder-drawing lands are provided on the other of the spaces between the forward soldering land group and the rearward soldering land group and in the tail-endmost portion of the rearward soldering land group to prevent solder bridges from being formed (for example, Japanese Patent Application Laid-open No. 2005-175186, PP. 1 to 3, FIGS. 1 to 11).
Moreover, one in which a solder drawing land is provided at a point where a front soldering land group and a rear soldering land group that is adjacent to the front soldering land group are adjacent to each other, and/or in a trailing area of the rear soldering land group, and the solder drawing land is formed with a slit substantially parallel to the lines of soldering lands of the front soldering land group or rear soldering land group that are adjacent to a front part of the solder drawing land has been available (for example, Japanese Patent Application Laid-open No. 2007-48874, PP. 1 to 4, FIGS. 1 to 4).
Furthermore, one in which a solder drawing land is provided at a point where a frontward soldering land group and a rearward soldering land group that is adjacent to the frontward soldering land group are adjacent to each other, and/or in a trailing area of the rearward soldering land group, the solder drawing land has first and second rearward solder drawing lands, the second rearward solder drawing land being formed larger than the first rearward solder drawing land and at least having its part formed rearward with respect to the direction of travel in soldering of the first rearward solder drawing land has been available (for example, Japanese Patent Application Laid-open No. 2000-40869, P. 5, FIGS. 1 to 2).
For the conventional printed wiring boards described above, elaborate management of a manufacturing process is required to maintain stable and high quality soldering that does not cause any solder bridges between leads of a quad flat package IC, and there has been a problem that it is difficult to maintain higher precision as the lead pitch is narrowed or when lead-free solder having poor solderability is used.